DK2985_C000 1..28 - AlSharqia Echo Club

28 Transesophageal Echocardiography(A)(B)TMFflowdirectionbaseline(C)TMFEA(E)LAAoLVRVLVOT(D)TMFEAFigure 2.5 Flow reversal on spectral display (aliasing). (A) Schematic drawing of spectral display. By lowering the baseline, the tip ofthe curve can be readjusted into the forward direction and maximal velocity can be calculated. (B) Pulsed-wave Doppler image of mitralflow with mitral regurgitation. The velocity of the forward flow is correctly estimated (0.45 cm/sec) but the high-velocity jet of regurgitation(5–6 m/s) is buried in the aliasing signal (arrow). The maximal velocity is unrecordable. (C) Mid-esophageal long axis view of themitral valve. The scale on the left is lower than the maximum mitral velocity. (D) This aliasing is eliminated by increasing the scalethrough baseline elevation. (E) Site of the transmitral pulsed-wave Doppler sampling (Ao, aorta; LA, left atrium; LV, left ventricle;LVOT, left ventricular outflow tract; RV, right ventricle; TMF, trans-mitral flow).the instrument can read. Three facts explain thisphenomenon:the sampling rate: the frequency overlap between PRFand Doppler shift giving rise to aliasing, asexplained earlier;the emitting frequency of the probe: for the sameDoppler shift, the transducer must sample twice asfast for a 5.0 MHz as for a 2.5 MHz probe; at thesame PRF, the maximum recordable velocity witha 5.0 MHz probe is half the velocity determined bya 2.5 MHz probe (7);the depth of the sampling gate: the deeper the interrogatedtarget, the longer the elapsed time betweentwo pulse emissions; the maximum recordable velocityis lessened when the PRF decreases (2.3 m/sat 8 cm with a 2.5 MHz probe and 0.65 cm/sec at16 cm with a 5.0 MHz) (5).